A true Christian is one who believes in what the Lord preached, which is to love one another, be just, love truth, and other such teachings of His Way.
In
Luke 10:30-37 the Lord gives an example of a priest, a rabbi, and a Samaritan.
Both the priest and Samaritan gave no love or mercy to their own injured countryman, while the Samaritan (an enemy to the Jews), nevertheless, believing in love and mercy, helped the injured man.
It doesn't matter what someone claims themselves to believe in; what matters is what their actions prove them to believe in.
The Samaritan, though never having heard of Christ, believed in Christ's Way of loving his neighbor.
Luke 10:30 And Jesus answering said, A certain man went down from Jerusalem to Jericho, and fell among thieves, which stripped him of his raiment, and wounded him, and departed, leaving him half dead.31 And by chance there came down a certain priest that way: and when he saw him, he passed by on the other side.
32 And likewise a Levite, when he was at the place, came and looked on him, and passed by on the other side.
33 But a certain Samaritan, as he journeyed, came where he was: and when he saw him, he had compassion on him,
34 And went to him, and bound up his wounds, pouring in oil and wine, and set him on his own beast, and brought him to an inn, and took care of him.
35 And on the morrow when he departed, he took out two pence, and gave them to the host, and said unto him, Take care of him; and whatsoever thou spendest more, when I come again, I will repay thee.
36 Which now of these three, thinkest thou, was neighbour unto him that fell among the thieves?
37 And he said, He that shewed mercy on him. Then said Jesus unto him, Go, and do thou likewise.